Rapid bacteriological metal extraction method

ABSTRACT

Method of rapid bacteriological extraction of metals from materials containing sulfides by subjecting to agitation a pulp comprising particles of said materials and an aqueous acid leaching medium including sulfide-oxidizing bacteria, while simultaneously aerating the pulp with air enriched with carbon dioxide.

United States Patent [72] Inventors Douglas W. Duncan West Vancouver, British COIIIIIIDE CeciletlfM. McCoran, mcouver, British 29111995 99k .392 3. [21] Appl. No. 707,501 [22] Filed Feb. 23, 1968 [45] Patented [73] Assignee Sept. 21, 1971 British Columbia Research Council Vancouver, British Columbia, Canada [54] RAPID BACTERIOLOGICAL METAL EXTRACTION METHOD 18 Claims, 7 Drawing Figs.

[52] U.S.Cl 75/101 [51] C22b 3/00 [50] Field ofSearch 75/101, 104, 97

COPPER LEACnlNG RATE (-11 8 o o o [56] References Cited UNITED STATES PATENTS 3,266,889 8/1966 Duncan-ct al .1 75/101 3,305,353 2/1967 Duncan m1. 75/101 3,347,661 10/1967 Mayling 75/104 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-E. L. Weise AtmrneyFetherstonhaugh & Co.

40 LEACHING RATES A A FUNCTION (E SULFIDE PULP DENSITY CO; ENRICHED AIR (1.0% AND UP TO lO/o], IMPROVED AGITATION OXYGEN ENRICMED (52%) AND c0; ENRICHED (10%) 1401mm. AGITATION CO ENRICHED AIR (O.l/o), IMPROVED AGlTATlON co ENRICHED AIR (0.1%) NORMAL AGITATION NORMAL AIR AND AGITATION PERCENT SUFIDE SOLIDS RELEASE RATE (mg/I PATENTED sEP21 IQYI SHEET 1 OF 3 LEACHING RATES A s A FUNCTION o F gggm: 93g ggggggy 5 co; ENRICHED AIR (|.0% AND up TO ifi /o), wmnovso Aen'AnmII G sOXY'G'EN mmcmzn (52%? AND cm 4 mmcaw G /o) Amwmcm w? J .I I w 1:0 ENRlCHEm 1m mmfimtm z 20m o w mmmsm N .I {5/ .J

35 |oo- & NORMAL ma mo AGiTATiON o o 0 I l l I I s I l 0 0.5 m as 2.0 25

PERCENT SUFBDE SQLRDS 79% EFFECT Qf CARBON momma commmmaow 9w LEACH RATE soo- 2am COPPER I I I I I I I I I I o l 2 a 4 5 6 7 a 9 l0 PERCENT CARBON DIOXIDE INVENVUIS DOUGLAS W. DUNCAN CECILE JM. McGORAN ATTOINEVS rz-lsovzzas mzulrtn ssrzl I97] SHEUZBF3 3mil-F821 OF OXYGEN CONCENTRATION ON LEAONING RATE T I I 70 SO ao'io so so I0 PERCENT OXYGEN IN ATMOSPHERE (BY VOLUME) o 2 3 3 ma d... 5&0

P 1 g LEACHING EFFECT 9f INITIAL ,n 4.0 pH 4.3

20 4O 6O 80 I00 I20 I40 M m m zoEEzuozou 3&

mvnnns I DOUGLAS I. DUNCAN CECILE I. I: GORAN HOURS OF LEAOI'IING ATTORNEYS PATENTED SEPZI I9?! (1507 21 35 SHEET 3 F 3 TEMPERATURE EFFECT 350* 300- i NORMAL AIR I% cARaou'oIoxmE v IMPROVED AGITATION 200" I o 3 uoRuAI. AIR,Ioz, I CARBON oIoxIoE u NORMAL AGITATION o E a: 0 NoRuIAI. AIR

NORMAL AGITATION o I I I I I I I I5 TEMPERATURE P0) g. f]. g. 7.

LEACHING COPPER CONCENTRATE LEAcIIme ZINC CONCENTRATE 20 40- hlaq 36.. I 346- E 32- z 3 9 I4- z 26- Z 2 E '2- S 24- K 5 Io- 20- u u g o o 8 C2) l6- m U o I I I I l I I l O I l I I I. I I I I 0 20 40 6O 80 I00 I20 I40 I 0 20 40 60' I00 I20 I40 I60 HOURS OF LEACHING HOURS OF LEAOHING INvENToRs DOUGLAS W. DUNCAN CECILEMI'IM. m oRAN ATTORNEVQ RAPID BACTERIOLOGICAL METAL EXTRACTION METHOD BACKGROUND OF THE INVENTION This invention relates to rapid microbiological methods for the extraction of metals from materials containing metallic sulfides, such as ores, concentrates and minerals.

The leaching of metals from sulfide-containing materials by bacteria, such as Thiobacillus ferrooxidans has been known and carried out artificially for a great many years. For years, the rates of extraction were impractically slow for commercial operations, taking 55 or more days to obtain small-quantities of the metals. A much improved process is described in U.S. Pat. No. 3,305,353, dated Feb. 21, 1967. This patented process increases the percentage of the metal released, and reduces the time to something of the order of days. The prior process will result in the microbiological release of copper from chalcopyrite at rates of 40 to 50 mg./l./hr. This is satisfactory for the release of expensive metals, such as uranium associated with pyrite or nickel from its sulfides, but it is economically marginal for the release of copper, and submarginal for the release of lower value metals, such as zinc.

During the oxidation of chalcopyrite (CuFeS the iron is oxidized from the ferrous to the ferric fonn and the sulfur is oxidized from sulfide to sulfate, thereby destroying the crystal lattice of the mineral and releasing the copper into solution. For each mole-equivalent of copper (63.5 g.) released, 2 moles of sulfide (64 g.) are oxidized. Since copper is more conveniently measured than sulfate, the solubilization of copper is followed as an effective measure of the oxidation of the chalcopyrite.

SUMMARY OF THE INVENTION Whereas the invention set out in U.S. Pat. No. 3,305,35 3 involved improvements in leaching rates over those of previous investigators by using the liquid-culture technique of agitating and aerating the minerals suspended in an aqueous medium in the presence of bacteria, the present invention builds on this prior process by optimizing certain factors affecting leaching.

These factors are:

1. Pulp density (ratio of mineral solids to the total weight in the fermentation). Mineral solids here refers to those sulfide minerals which may be attacked by the bacteria and not other minerals which are inert in this regard and which may be present if an impure mineral concentrate or ore is being leached.

2. The percentage of carbon dioxide present in the artificial" atmosphere being used to aerate the fermentation, the aeration being stipulated in the above-mentioned patent.

3. In some instances, the percentage of oxygen present in the artificial atmosphere being used to aerate the fer mentation.

A method according to the present invention of rapid bacteriological extraction of metals from materials containing metallic sulfide, comprises making a pulp of a density of from about 0.5 percent and up of the metallic sulfide and an aqueous acid leaching medium comprising sulfuric acid, sulfide-oxidizing bacteria and nutrient for the bacteria. This density is given relative to the metallic sulfide present and is not concerned with the nonsulfide materials that may be in the pulp. This pulp is subjected to agitation to maintain the particles suspended therein, and is simultaneously aerated with air enriched with carbon dioxide so as to contain about 0.1 to about percent of this gas. This enables the bacteria rapidly to oxidize the sulfide. The pH of the solution may range from about 1.5 to about 3.5, but it is preferable to maintain the pH between about 2.5 and about 3.0. The temperature may range from 10 to 40 C., but it is preferably in the range from about hydrogen phosphate, magnesium chloride, calcium nitrate and potassium chloride.

The concentration of the leaching medium is preferably from about 1.0 to about 2.0 percent sulfide solids, but may range from about 0.5 to about 20 percent. The length of time of the agitation and aerating will depend upon the type of material being treated, and upon the percentage of the metals it is desired to release from the material.

The agitation should be quite vigorous. It has been found that with proper agitation, a very high percentage of the metals present canbe released at'a rapid rate. 0n the other hand, extremely good resultscan be attained when the agitation is reduced and the air used in the aeration of the pulp is enriched by increasing the percentage of oxygen thereof anywhere from 21 to about 60 percent.

Metal release rates are obtained with the present method which are improved considerably over those of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph illustrating the rate of metal release by the present method as compared to that of the method of the prior art,

FIG. 2 is a graph illustrating effect of carbon dioxide concentration on the leach rate,

FIG. 3 is a graph illustrating the effect of using oxygen-en riched air under some circumstances,

FIG. 4 graphically illustrates the pH effect on the leaching,

FIG. 5 is a graph illustrating the effect of temperatures on the process,

FIG. 6 graphically illustrates an example of copper leaching time and concentration, and

FIG. 7 graphically illustrates an example of zinc leaching time and concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method according to the present invention covers the extraction by means of bacteria of metals from materials containing metallic sulfide, such as copper, zinc, uranium, arsenic, nickel, gold, silver, cobalt, tin, cadmium and the rare earth metals as listed in the periodic table. For the sake of convenience, the method will be described in detail relative to the extraction of copper from chalcopyrite.

The sulfide-containing material is ground to a particle size which is usually less than 325 mesh and preferably less than 400 mesh. The particulate material is mixed with an aqueous acid leaching medium to make a pulp of a density of from about 1.0 percent and up. Any suitable leaching medium may be used for this purpose, such as, for example, a medium containing 3.0 g. of ammonium sulfate, 0.1 g. of potassium chloride, 0.5 g. of dipotassium hydrogen phosphate, 0.5 g. of magnesium sulfate heptahydrate, and 0.1 g. of calcium nitrate per liter of water. The pH of the medium should 3.0, from about 2.5 to about 3.0, although values as low as 1.5 and as high as 3.5 can be used. This is an acid solution which is compatible with sulfide-oxidizing bacteria. The bacteria in the medium should be those classified as Thiobacillusferrooxidans, and in some instances it may be preferable to add a surfactant,

such as sorbitan polyoxyethylene monolaurate. The pulp is subjected to sufficient agitation to maintain the particles suspended in the medium, and the pulp is simultaneously aerated with air enriched with carbon dioxide so as to contain about 0.1 to about 10 percent of this gas. In the method of U.S. Pat. No. 3,305,353 the pulp density was about 1.33 perleaching atmosphere requires a minimum pulp density of about 0.5 percent if pulp density is not to be a rate-limiting factor. If oxygen-enriched air is used, the pulp density should be at least 0.89 percent, a level similar to that required with normal air and improved agitation. Thus, the accelerated rates achieved by this invention require a combination'of minimum pulp densities and extra carbon dioxide with or without extra oxygen in the leaching atmosphere. If the pulp is extremely well agitated, the use of additional oxygen is not required, but carbon dioxide is still necessary. Under such conditions minimum sulfide pulp densities of about 1.2 percent are required, and leach rates. as high as 355 mg./l./hr. are achieved. However, if the agitation is not very efi'icient, then it is highly desirable to enrich the aerating medium with oxygen.

It has been found by experimenting that, when dealing with chalcopyrite, the addition of 0.1% CO, produced average leach rates of 250 mg. of copper released per liter per hour,

whereas the 1% CO and above the average rate was 358 mg./l./hr. Using zinc sulfides, the average release rates when 0.1, l and CO was used were 400, 627, and 630 mg./l./hr. respectively. It is obvious that 0.1% CO, is not very good from an economical standpoint but it is better than normal air.

The results of variations in the present method are illustrated in the graphs of the drawings and in the following examples:

EXAMPLE I When 8.0 g. of a chalcopyrite concentrate containing 28 percent copper, was leached in 75 ml. of a nutrient medium containing 3.0 g./l. (NI-I SO 0.l g./l. KCl, 0.5 g./l. of K l'l- P0 0.5 g./l. MgSO -7H,O and 0.1 g./l. Ca(NO at an initial pH of 2.8 and a temperature of 35 C., with aeration and agitation supplied by means of a gyratory shaker oscillating at 160 r.p.m., the leach curve shown in FIG. 6 was obtained. The atmosphere used for aeration contained 21 percent oxygen and 1 percent carbon dioxide. The rate of copper release was 360 mg./l./hr. (FlG. l) and the final copper concentration was 16 g./l. Leaching was essentially complete in this batch process within 60 hours. The amount of auxiliary nutrients indicated above is considerably in excess of what is needed.

In other experiments the same experimental conditions were used except that additional feed material was added to the flask after 40 and 60 hours of leaching. Under these condition the rapid rate of copper release continued beyond the 60- hour mark and the copper concentration obtained exceeded 30 g./l. indicating that the appropriate addition of feed and removal of copper-containing solution, a continuous system is possible.

EXAMPLE 2 In this experiment the leaching conditions were exactly the same as in example 1 with the exception that nutrient medium only contained 0.3 g./l. (NH SO, and 0.06 g./l. K lHPO The leach curve obtained was identical to that shown in FIG. 6.

EXAMPLE 3 When 8.0 g. of a zinc sulfide concentrate containing 46.6 percent zinc was leached in 75 ml. of a nutrient medium containing 3.0 g./l. (NI-M 80 0.1 g./l. of KCl, 0.5 g./l. of K i-I- PO 0.5 g./l. of MgSO -7I-I O and 0.1 g./l. of Ca(NO at an initial pH of 2.8 and 35 C with aeration and agitation supplied by a gyratory shaker operating at 160 rpm, the leach curve shown in FIG. 7 was obtained. The air used for aeration contained 21 percent oxygen and 1 percent carbon dioxide. The rate of zinc release was about 620 mg./l./hr. and the zinc concentration was in excess of 40 g./l.

EXAMPLE 4 When 8.0 g. of chalcopyrite concentrate containing 28 percent copper, was leached in 75 ml. of a nutrient medium containing 3.0 g./l. (NHQ SQ 0.1 g./l. KCl, 0.5 g./l. of K HPO 0.5 gJl. MgSOfll-ifi and 0.1 g./l. Ca(NO at an initial pH of 2.8 and a temperature of 35 C., with air containing 21 per cent oxygen and 10 percent carbon dioxide and with considerably less agitation thanset out in example 1, a leach curve similar to the one shown in FIG. 6 was obtained, except that the rate of copper release was only about mg./l./hr. When the percentage of oxygen in the air was increased, the rate of copper release increased as shown in FIG. 3.

FIG. 1 illustrates results attained by the process of example 1, but with the changes indicated in the graph. The copper and zinc lines in the graph of FIG. 2 indicate the results of examples l and 3, respectively. HO. 4 indicates the different results attained with the process of example 1 by varying the initial pH of the leaching medium. FIG. 5 compares the different results attained in the process of example 1 by the use of normal air and normal agitation, carbon dioxide enriched air and normal agitation, and carbon dioxide enriched air and improved agitation at different temperatures.

We claim:

l. A method of rapid bacteriological extraction of metals from materials containing metallic sulfides, which process comprises making a pulp of a sulfide density of at least about 0.5 percent and up of particles of materials containing said metallic sulfides and an aqueous acid leaching medium; said medium comprising sulfuric acid, sulfide-oxidizing bacteria and nutrient for said bacteria; subjecting the pulp to agitation to maintain the particles suspended in the medium, and simultaneously aerating the pulp with air enriched with carbon dioxide so as to contain about 0.1 to about 10 percent of said gas, thus enabling the bacteria rapidly to oxidize said sulfide.

2. A method as claimed in claim 1 wherein said particles of sulfide-containing materials are less than 325 mesh in size.

3. A method as claimed in claim ll wherein said bacteria comprise Thiobacillusferrooxidans.

4. A method as claimed in claim 1 wherein the pH of the leaching medium is from about 1.5 to about 3.5.

5. A method as claimed in claim ll wherein the pH of the leaching medium is from about 2.5 to about 3.0.

6. A method as claimed in claim 1 wherein the sulfide pulp density of the leaching medium is from about 0.5 to about 20 percent.

7. A method as claimed in claim 1 wherein the sulfide pulp density of the leaching medium is from about 1.0 to about 2.0 percent.

8. A method as claimed in claim 1 wherein the temperature during agitation and aeration is maintained from about 10 to about 40 C.

9. A method as claimed in claim 1 wherein the temperature during agitation and aeration is maintained from about 30 to about 35 C.

10. A method as claimed in claim 1 in which said air aerating the pulp contains from about 21 percent to about 60 percent oxygen.

lll. A method as claimed in claim 10 wherein said particles of sulfide-containing materials are less than 325 mesh in size.

12. A method as claimed in claim 10 wherein said bacteria comprise Thiobacillusferrooxidans.

13. A method as claimed in claim 10 wherein the pH of the leaching medium is from about L5 to about 3.5.

14. A method as claimed in claim 10 wherein the pH of the leaching medium is from about 2.5 to about 3.0.

15. A method as claimed in claim 10 wherein the sulfide pulp density of the leaching medium is from about 0.5 to about 20 percent.

16. A method as claimed in claim 10 wherein the sulfide pulp density of the leaching medium is from about 1.0 to about 2.0 percent.

17. A method as claimed in claim 10 wherein the temperature during agitation and aeration is maintained from about 10 to about 40 C.

18. A method as claimed in claim 10 wherein the temperature during agitation and aeration is maintained from about 30 to about 35 C. 

2. A method as claimed in claim 1 wherein said particles of sulfide-containing materials are less than 325 mesh in size.
 3. A method as claimed in claim 1 wherein said bacteria comprise Thiobacillus ferrooxidans.
 4. A method as claimed in claim 1 wherein the pH of the leaching medium is from about 1.5 to about 3.5.
 5. A method as claimed in claim 1 wherein the pH of the leaching medium is from About 2.5 to about 3.0.
 6. A method as claimed in claim 1 wherein the sulfide pulp density of the leaching medium is from about 0.5 to about 20 percent.
 7. A method as claimed in claim 1 wherein the sulfide pulp density of the leaching medium is from about 1.0 to about 2.0 percent.
 8. A method as claimed in claim 1 wherein the temperature during agitation and aeration is maintained from about 10* to about 40* C.
 9. A method as claimed in claim 1 wherein the temperature during agitation and aeration is maintained from about 30* to about 35* C.
 10. A method as claimed in claim 1 in which said air aerating the pulp contains from about 21 percent to about 60 percent oxygen.
 11. A method as claimed in claim 10 wherein said particles of sulfide-containing materials are less than 325 mesh in size.
 12. A method as claimed in claim 10 wherein said bacteria comprise Thiobacillus ferrooxidans.
 13. A method as claimed in claim 10 wherein the pH of the leaching medium is from about 1.5 to about 3.5.
 14. A method as claimed in claim 10 wherein the pH of the leaching medium is from about 2.5 to about 3.0.
 15. A method as claimed in claim 10 wherein the sulfide pulp density of the leaching medium is from about 0.5 to about 20 percent.
 16. A method as claimed in claim 10 wherein the sulfide pulp density of the leaching medium is from about 1.0 to about 2.0 percent.
 17. A method as claimed in claim 10 wherein the temperature during agitation and aeration is maintained from about 10* to about 40* C.
 18. A method as claimed in claim 10 wherein the temperature during agitation and aeration is maintained from about 30* to about 35* C. 